Method for removing wax



July 2l, 1936. U, B BRAY E-r AL 2,048,244

METHOD FOR REMOVING WAX Filed Deo. 18, 1933 IJ l 1 i? ewaxed 01'/ mwen? 42 f Wqry 0277 gz uen? iin/ /H /10 LLLLLLL INVENTORS J/rzc Bray Mana/d5. Carr u .4 TTORNEY Patented -July 21, 1936 METHOD ,FOR REMOVING WAX Ulric B. Bray, Palos Verdes Estates, and Donald E. Carr, Naples, Calif., assignors to Union Oil Company of California, Los Angeles, Calii., a corporation of California Application December 18, 1933, Serial No. 702,986

10 Claims.

The present invention relates to the art o1' separating wax from wax-bearing oils, and more particularly it pertains to the withdrawal of wax from iilters used for such separation.

It is well knownv that the presence of wax or waxy fractions in lubricating oils produced or obtained from wax-containing crude oils lowers the quality and value of such lubricating oils. This is due to the fact that such presence of wax causes the congealing of the lubricating oil at a comparatively high temperature thus preventing proper lubrication. It has therefore been the custom to remove the wax from the lubricating oil fractions containing the same. Recently, a method has been developed whereby, briey stated, the removal of the wax from the waxbearing oils is produced by the use of propane or of similar liqueiied but normally gaseous hydrocarbons, as for example liquid butane, pentane, etc. According to this method the oil to be dewaxed is mixed with a proper quantity of such liqueed but normally gaseous hydrocarbon, and

the mixture is then chilled to a temperature sufcient to cause the precipitation of the wax. The agglomeration of the wax from the waxoil-solvent mixture may also be aided by treatment with electricity. The wax thus agglomerated and precipitated is then removed from the oil-solvent mixture by cold settling, illtration or centrifuging. In view of the long period of time necessary for the removal of wax by the settling method, and due to the high cost of centrifuging the mixture, it has been found that the iiltration method is most suitable for such removal of the agglomerated wax. However, the wax cake obtained during such ltration and especially at the conclusion of the washing cycle, i. e. after the washing of the lter-cake with propane or another hydrocarbon solvent for the removal therefrom of the oil still adhering to the Wax, is very hard and is in a state in which it is difcult to remove it from the filter plates, the particles of wax adhering tenaciously to each other and to the lter plates.

It is therefore an object of the present invention to provide a method of easily removing the wax precipitated on the lter plates.

It is another object to treat the wax iilter-cake so as to admit a rapid and easy removal thereof from the filter plates.

It has now been discovered that the waxy phase obtained in the dewaxing of wax-bearing oils by means of liqueiied propane contains a comparatively large proportion of such propane. This propane is in true solution in the Wax and does not merely constitute an occluded solvent. It has been further discovered that the evaporation of such propane from its true solution in the wax leaves the latter in a porous expanded form which is easily handled.v 'I'his is probably due to the fact that the diierential or uneven evaporation of the propane from. the di'erent layers within the filter-cake creates di'erential pressures therein. This in turn produces an explosive or bumping effect within the cake with the result that rapid elorescence of the wax takes place.

The present invention therefore resides in treating the wax filter-cake so as to evaporate therefrom the liquid propane or a similar liqueed but normally gaseous hydrocarbon, and thereby leave the wax in a condition in which it is readily removable from the iilter plates.

The invention further resides in ltering the mixture of a waxy oil and solvent, and subsequently treating the thus produced lter-cake to evaporate therefrom the liquid solvent remaining in solution in the wax phase. This evaporation of the liquid solvent, as for example of the liquid propane, may be carried out in a variety of ways, as for instance by release of pressure, by the use of vacuum, by mechanical heating, or by passing an electric current through the frame or metal parts of the lter plates or leaves.

As a specic example, a waxy oil is dissolved in liquid propane or a similar liqueed but normally gaseous hydrocarbon in the proportion of about one part of the waxy oil to from three to nine parts of the diluent-solvent, this proportion depending upon the character of the oil being treated, type of diluent used, degree of dewaxing desired, etc. The mixture thus obtained is maintained under a pressure suicient to keep the diluent in a liquid state under ordinary temperatures, said pressure ranging anywhere from 25 to 200 lbs. per square inch. Thereupon, the solution is chilled as by' lowering the pressure and vaporizing a portion of the liqueiied but normally gaseous hydrocarbon used as the diluent. This chilling is carried down to temperatures sufcient to cause the above-mentioned precipitation or agglomeration of the wax in the oil, such temperatures ranging from +10 F. to -40 F. depending upon various conditions such as the character of the waxy oil and of the diluent, the ratio-of one to the other, degree of dewaxlng desired, etc. After such chilling of the diluted oil the mixture is conveyed under pressure through a lter press wherein the wax is caused to deposit in the form of a compact cake on the lter leaves or plates. This stantially equal to that mentioned hereinabove.,

In view of the fact that the wax cake thus pro- ,duced is hard, and since it is exceedingly diilicult to remove it, due to its tenacity, from the iilter leaves, the wax is then treated as above described to cause an evaporation of the liquid propane in solution in said wax.

Thus. the iiltercake in the filtration chamber may be heated, as for example by blowing a heat- -ed gas, to a temperature sumcient to volatilize the liquid propane Ai'n solution in the wax. Also, the pressure in the filtration chamber may be lowered to produce such evaporation of the propane. :If necessary, a partial vacuum may be created for the same purpose. The evaporation of the propane causes a rapid eiilorescence or powderingof the wax, and leaves the latter in a porous and expanded form so that the removal of such wax may be carried out very easily, as by tamping on the filter plates. l

It is to be noted that the heating of the wax must be carried only to a temperature of evaporation of the solvent. Further heating is detrimental in that it dissolves the wax thus increasing the diiiiculty of its removal from the iiltration chambers.

It is obvious that the above operations may bel carried out in a number of apparatuses. However, for the purpose of explaining more fully the manner of carrying out the present process, reierence will be had to the drawing, Figure I of which discloses a structure for an uninterrupted dewaxing of the oil according to the process described herein, while Figure II shows a structure which may be used for the continuous filtering and removal of wax from a wax-bearing oil.

Referring to Figure I, the filter chamber I0 is provided with a plurality of vertically disposed filter elements I I. The oil to be dewaxed is introduced into chamber I0 through a. line I2 provided with a valve I3, while the dewaxed oil is Withdrawn through pipe I5 equipped with a valve I6. A line I1, having a valve I8 thereon, leads from the upper part of the structure, while a screw conveyor 20 communicates the lower end of the filter chamber I0 with a wax discharge line 2 I, said line being also provided with a valve 22.

In operation, a waxy oil, preferably maintained at superatmospheric pressure, commingled in a proper ratio with a diluent, such as liquid propane, and chilled to a temperature at which the desired amount of wax is precipitated out of solution, is introduced into filter chamber l0 through line I2. The wax precipitates on the illter elements I I, while the thus dewaxed oil-diluent mixture is withdrawn through line I5. When the filter elements become clogged with Wax, valves I3 and I6 on lines I2 and I5, respectively, are

ing of the wax on the filter element 35.

a diluent prior to the release of pressure. Such a procedure removes from the wax any oil stili adhering thereto. It is also obvious that, instead of the above-described pressure reduction, the` evaporation of the solvent in the wax may be ac- 5 complished by heating the filter plates II, asby passing an electric current therethrough.

It is sometimes advantageous, as well as desirous, to operate the dewaxing of waxy oils in a continuous manner. Figure II shows a struc- 10 ture which may be used for such continuous illtiation, 'and which discloses a means ior the breaking up of the compa-ct wax deposited on a filter drum. In this figure, the wax-bearing oil is introduced under pressure through line 2l 15 into a mixer 26 wherein it is commingled with a diluent, such as propane, brought to said mixer through line 21. The thus obtained mixture is conveyed through line 29 to a chiller Il wherein said mixture is chilled'to a temperature at which 2o the wax falls out of solution. The chilled mixture is then conveyed through line 3| into the lower portion of a filter shell 33, which encloses a rotatable perforated drum 34 having a filter element 35 on its periphery. The filtering drum 25 34 is divided into a plurality of segments by means oi imperforated plates 36, these segments opening into a valve assembly located along the axis of the filter drum 34. This valve assembly consists of a valve 3l connected to line 3l, and valve 40 connected to line 4I. Lines 39 and 4I are also provided with valves 42 and 43, respectively. The purpose of the valve assembly and of lines 39 and 4I will be described more fully hereinbelow in connection with the description 35 of the operations of the structure.

A portion of the space between the shell 33 and the periphery of the drum 34 is separated or isolated from the rest of such space by means of longitudinal plates 45 and 46. Thechamber 41 thus produced is provided with a pressure discharge line 49 carrying a valve 50. This chamber is further provided with a wax-removing scraper 52 abutting against filter element 35, the scraped material being removed by means of a scroll conveyor 53 and conduit 54 to a wax pot not shown in the drawing.` Optionally, a line 56. may be provided for the introduction o! naphtha, or of a similar substance, for the wash- In operation, the oil-wax-diluent mixture or slurry is introduced into the lower portion of shell 33 through line 3|, the rate of introduction of the slurry being regulated to maintain a predetermined level in said shell. The space above the slurry is maintained at a pressure to prevent the evaporation of the diluent. The illter drum 34, together with the filter element, are slowly rotated. By maintaining a pressure diiierential across said lter element, filtration will occur 00 in the segments dipping into the slurry. The filtrate, consisting of the dewaxed oil and the diluent, passes through the filter element and flows into the control -valve 38 and out through line 39, while the wax accumulates in the form 65 of a compact cake on the surface of the filter element 35. The continuous rotation of the illter drum 34 then brings the wet filter cake into the space above the slurry. Here, the wax may be optionally washed by naphtha or the like intro- 70 duced through line 55, said washing agent, together with any oil adhering to the wax, being withdrawn from the system through valve 40 and line 4| provided with a valve 43.

Periodically, when the segmental walls 3l of 75 the illter drum 34 come in juxtaposition with variations may be made by those skilled in the art within the scope of the appended claims.

We claim:

1. A method for separating wax fromfwaxbearing oils which comprises commingling waxbearing oil with a liqueiied normally gaseous diluent, chilling the mixture to a temperature at which wax precipitates from solution, ltering said chilled mixture to separate oil andA diluent from the wax deposited in the filtration zone, withdrawing the separated oil and diluent from the ltration zone, suddenly evaporating the diluent still remaining in the ltered wax cake by reducing the pressure thereon and thereby causing the wax cake to become porous, expanded and easily friable and withdrawing the thusconditioned wax cake from said illtration zone.

2. A method as in claim 1 in which the pressure on the wax cake is reduced to a vacuum.

3. A method for separating wax from waxbearing oils which comprises commingling waxbearing oil with a liquefied normally gaseousvdiluent, chilling the mixture to a temperature at which wax precipitates from solution, ltering said chilled mixture under superatmospheric pressure to separate oil and diluent from.the wax deposited in the filtration zone, withdrawing the separated oil and diluent from the filtration zone, suddenly evaporating the diluent still remaining in the filtration wax cake by reducing the pressure thereon and thereby causing the wax cake to become porous, expanded and 5 easily friable and withdrawing-the thus condi- 4. A method as in claim 3 in which the evaporation of the waxcalfe is accomplished by releasing the pressure in the filtration zone.

5. A method as in claim 1 in which the diluent is a liquefied normally gaseous hydrocarbon. 5

6. A method as in claim 1 in which the diluent is liquid propane.

7. A method for separating wax from waxbearing oils which comprises commingling waxbearing oil with a'llqueiied normally gaseous diluent, chilling the mixture to a temperature at which wax precipitates from solution, ltering said chilled mixture under a pressure of about 25 to 50 pounds per square inch to separate oil and diluent from the wax deposited in the filtration zone, withdrawing the separated oil and dlluent from the iiltration zone, suddenly evaporating the diluent still remaining in the filtered wax cake by reducing the pressure thereon and thereby causing the wax cake to become porous, expanded and easily friable and withdrawing the thus conditioned wax cake .from said iiltration zone.

8. A method for separating wax from waxbearing oils which comprises commingling waxbearing oil with a liqueiied normally gaseous diluent, chilling the mixture to a temperature at which wax precipitates from solution, filtering .said chilled mixture to separate oil and diluent from the wax deposited in the filtration zone, 30 withdrawing the separated oil and diluent from the filtration zone, heating the wax cake to a temperature suilicient to vaporize the diluent from the wax cake but to a temperature insuiilicient to melt the wax and thereby causing the wax cake to become porous, expanded and easily friable and withdrawing the thus conditioned wax cake fronr'said filtration.

9. A method as in claim 8 in which the diluent is a liqueiled normally gaseous hydrocarbon. 40 10. A method as in claim 8 in which the diluent is a liquid propane.

ULRIC B. BRAY.

DONALD n. oma.

CERTIFICATE oF CORRECTION.

Patent Nq. 2,048,244. July 21, 193e.

ULRIC 13. BRALET AL.

It iS hereby Certified that erro'r appears in the printed specification of the above numbered. patent requiring correction as follows; Page 2, first column,v line 40, for "uninterrupted" readV interrupted; and that the said Letters Patent should be read ,with this correction therein that the same may conform to the record of the case in the Patent Office.

' Signed and sealed this 16th day of February, A.D. 1937.

Henry. Van Arsdale (Seal) Acting Commissioner of Patents. 

